In the printing industry, a desired image is repeatedly printed on a continuous web or substrate such as paper. In a typical printing process, the continuous web is slit in the longitudinal direction (the direction of web movement) to produce a plurality of continuous ribbons. The ribbons are aligned one on top of the other, folded longitudinally, and then cut laterally to produce a plurality of multi-page, approximately page-length segments, each of which is termed a “signature”. The term signature also encompasses a single printed sheet that has or has not been folded.
To monitor the print quality on a signature, various methods may be used to measure the color quality of the printed signature. One method includes printing a color bar having multiple color patches of different known colors and intensities such that the color quality of the color bar can be measured and compared to a standard, the color bar being representative of the color quality of the printed signature. By so doing, the color quality of the printed signature may be measured by utilizing an image processing apparatus, e.g. a camera, to acquire an image of a single point of the printed color bar. Current image processing apparatus systems for measuring the color quality may utilize a CCD color camera having red, green, and blue channels (i.e. an RGB camera).
There may be a difficulty with current image processing systems, especially with those utilizing an RGB camera, in developing color transforms to transform from the RGB filters to the density or colorimetry filters. This may limit the number of ink colors than can be effectively monitored using the image processing system.